SPECIAL BRASSES 227 exactly, acidified with 8-10 drops of 2N-hydrochloric acid, heated to 50°, treated with about 2% (with reference to the volume of the liquid) of ammonium chloride, and saturated with hydrogen sulphide at 50°. When the zinc is completely precipitated, the zinc sulphide is allowed to settle at a moderate temperature, and is then filtered off, washed with aqueous hydrogen sulphide containing 2 grams of ammonium chloride per 100 c.c. and weighed as zinc sulphide, after being heated in a current of hydrogen in presence of sulphur : ZnS x 0-6709 = Zn. 6. Determination of the Nickel.—The filtrate from the zinc precipi- tate is boiled to expel hydrogen sulphide, concentrated, rendered faintly alkaline with ammonia, and the nickel precipitated with alcoholic dimethyl- glyoxime solution (see Analysis of Nickel Steel and of Argentan). 7. Determination of the Arsenic, Sulphur and Bismuth.—The methods given for the analysis of copper (q.v.) are followed. 8. Determination of the Phosphorus.—See Analysis of Phosphor Bronze. The ordinary brasses, besides copper and. zinc, often contain small quan- tities of lead and iron (sometimes up to i%), in some cases tin (0-5-1%) and nickel (0-1-0-3%) and, in general, the impurities present in the copper and zinc used in their preparation. A good brass should exhibit a fracture of uniform colour and fine and homo- geneoxis grain. It should not contain more than 0-01% of antimony, as other- wise it is brittle and unfit for hammering ; it should not contain more than 0-01% of bismuth or 0-1% of arsenic. The mean percentage compositions of some of the commoner commercial brasses are as follows : TABLE XXII Composition of Brasses Variety. Cu Zn Pinchbeck, tombac, Mannheim gold (for cheap jewellery) Brass for sheets and plates........ Brass for tubes............ Brass for casting........... Brass for wire............ White brasses (Fontammoreau bronzes) .... Brasses for welding.......... 85-95 60-72 65-70 66-67 60-67 I-IO 34-90 5-15 28-40 3°-35 33-34 33-40 90-991 10-66* SPECIAL BRASSES By this name are indicated those alloys of copper and zinc which con- tain small quantities of one or more other elements (especially lead, tin, iron, manganese, aluminium) introduced for the purpose of 'imparting special properties. The most important are as follows, 1 Often contains 1-2% of lead. contains, $,lso small quantities of timprous sulphide : Cu2S X 0-7986 = Cu.